Dynamic and Thermodynamic Controls on Deep Convection in Organization of Tropical East Pacific Convection (OTREC)

热带东太平洋对流组织（OTREC）中深层对流的动态和热力学控制

• 批准号: 1758603
• 负责人: Adam Sobel
• 金额: $ 53.2万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-03-15 至 2024-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1758603&HistoricalAwards=false
• 关键词: Dynamic; Thermodynamic; Controls; Deep; Convection

This grant supports work on the Organization of Tropical East Pacific Convection (OTREC) field campaign. The campaign seeks to understand the formation and development of tropical convective clouds and associated heavy rainfall in the adjacent but distinct regions of the eastern equatorial Pacific and the southwest Caribbean, along with their evolution over the intervening portions of Central America and Colombia. The campaign also examines the genesis and evolution of easterly waves, large westward-moving atmospheric disturbances (wavelengths of about 2,000 km) which occur on a weekly basis in the Caribbean and eastern Pacific. The full set of campaign grants is discoverable on the nsf.gov/awardsearch webpage by a keyword search on "OTREC".Tropical convection plays a critical role in earth's climate system and is also responsible for extreme precipitation and hurricane formation. Easterly waves are of particular interest for weather forecasting given their tendency to spawn hurricanes. More generally, tropical convection is an engine of weather and climate worldwide yet poorly understood and difficult to simulate. Work leading to better representation of tropical convection in weather and climate models can thus lead to better weather forecasts and impact assessments, both for the public and decision makers. Aside from the societal relevance of the science, the campaign features several education and outreach activities. These including support for undergraduate participation and production of short documentary videos for use in classroom teaching and informal science education. In addition, the Principal Investigators (PIs) maintain a blog during the period just before, during, and just after the field campaign, helping to communicate the science to a broader audience. The award also provides funding for the education of a graduate student and to bring three additional graduate students to the campaign, allowing them to gain valuable experience in fieldwork.The eight week campaign deployment consists primarily of a set of 20 flights in the Gulfstream V research aircraft maintained by the National Center for Atmospheric Research. The campaign uses an airport in Costa Rica for easy access to the equatorial Pacific and southwest Caribbean study regions, and conditions in these regions are sampled using dropsondes and a wing-mounted W-band radar. Dropsondes contain the same instrument package as standard weather balloons, only dropped from an aircraft (in this case from about 40,000 feet) with a small parachute. The radar determines cloud properties such as the relative abundance of ice particles versus liquid droplets, and uses Doppler shift to measure updraft and downdraft speeds in clouds. The aircraft sampling is augmented by observations collected at ground sites in Costa Rica and Colombia.Despite intensive study we still lack a satisfactory theory for how environmental conditions determine when and where tropical convection will form, how long it will last, how much it will expand and organize, and how much rain it will produce. Over the eastern Pacific tropical convection occurs in a narrow east-west strip a few degrees north of the equator, in a region where near-surface winds come together in an intertropical convergence zone (ITCZ). The near-surface wind convergence is a consequence of a strong north-south sea surface temperature (SST) contrast between the "cold tongue" along the equator and the warmer waters to the north. Surface winds near the equator tend to blow across SST contrasts and converge over the warmer water, and surface convergence induces rising motions favorable to convection.But the PIs argue against the notion that convection in the eastern Pacific ITCZ is driven primarily by surface convergence, pointing out that surface convergence does not automatically result in strong convection and heavy rainfall. Instead they hypothesize that thermodynamic factors including convective available potential energy (CAPE), convective inhibition (CIN), and the influence of moisture through entrainment and downdrafts are key to understanding convection in the region.The project also considers convection over the southwest Caribbean, where convection occurs despite a lack of SST contrasts and a relatively dry atmosphere. The PIs suggest that convection in these unfavorable conditions constitutes a self-sustaining equilibrium state which can develop given the right initial state, although the same environmental conditions would equally favor suppressed convection. Such multiple equilibrium behavior is seen in idealized models and has been associated with self-aggregation in cloud resolving models, and the PIs hypothesize that it is implicated in the active and suppressed phases of easterly waves.The research is conducted using data collected during the campaign in combination with a variety of numerical models including a cloud resolving version of the Weather Research and Forecasting (WRF) model. The PIs have several strategies for representing the relevant dynamics and thermodynamics in an idealized form, often using a small doubly-periodic domain. Observational comparisons use data from OTREC as well as earlier field campaigns (EPIC and TEPPS).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

这笔赠款支持热带东太平洋对流组织 (OTREC) 实地活动的工作。 该活动旨在了解东赤道太平洋和西南加勒比地区相邻但不同地区的热带对流云和相关强降雨的形成和发展，以及它们在中美洲和哥伦比亚中间部分的演变。 该活动还研究了东风波的起源和演变，以及每周在加勒比海和东太平洋发生的大型向西移动的大气扰动（波长约 2,000 公里）。全套活动资助可在 nsf.gov/awardsearch 网页上通过“OTREC”关键字搜索找到。热带对流在地球气候系统中发挥着至关重要的作用，也是极端降水和飓风形成的原因。 由于东风浪容易产生飓风，因此天气预报特别感兴趣。 更一般地说，热带对流是全球天气和气候的引擎，但人们对它知之甚少且难以模拟。 因此，在天气和气候模型中更好地表示热带对流的工作可以为公众和决策者带来更好的天气预报和影响评估。 除了科学的社会相关性之外，该活动还开展了多项教育和外展活动。 其中包括支持本科生参与和制作纪录片短片，用于课堂教学和非正式科学教育。 此外，首席研究员 (PI) 在实地活动之前、期间和之后都会维护一个博客，帮助向更广泛的受众传播科学知识。 该奖项还为一名研究生的教育提供资金，并让另外三名研究生参加该活动，使他们能够在实地工作中获得宝贵的经验。为期八周的活动部署主要包括由国家大气研究中心维护的湾流 V 研究飞机的 20 次飞行。 该活动利用哥斯达黎加的一个机场，方便进入赤道太平洋和西南加勒比研究区域，并使用下投探空仪和机翼安装的 W 波段雷达对这些区域的情况进行采样。 空投探空仪包含与标准气象气球相同的仪器包，仅使用小型降落伞从飞机上（在本例中从大约 40,000 英尺处）投下。 雷达确定云的特性，例如冰颗粒与液滴的相对丰度，并使用多普勒频移来测量云中的上升气流和下降气流速度。 飞机采样得到了在哥斯达黎加和哥伦比亚地面站点收集的观测结果的增强。尽管进行了深入的研究，但我们仍然缺乏令人满意的理论来解释环境条件如何决定热带对流何时何地形成、持续多久、扩展和组织的程度以及产生多少降雨。 东太平洋上空的热带对流发生在赤道以北几度的一条狭窄的东西向地带，该区域的近地表风在热带辐合带（ITCZ）中汇聚。 近海面风辐合是赤道沿线“冷舌”与北部温暖水域之间强烈的南北海面温度（SST）对比的结果。赤道附近的地表风倾向于吹过海温对比并在温暖的水面上汇聚，而地表辐合会引起有利于对流的上升运动。但PIs反对东太平洋ITCZ的对流主要由地表辐合驱动的观点，指出地表辐合不会自动导致强对流和强降雨。 相反，他们假设热力学因素，包括对流可用势能 (CAPE)、对流抑制 (CIN) 以及夹带和下降气流对水分的影响，是理解该地区对流的关键。该项目还考虑了西南加勒比地区的对流，尽管缺乏海温对比和相对干燥的大气，但对流仍然发生。 PI表明，在这些不利条件下的对流构成了一种自我维持的平衡状态，在给定正确的初始状态的情况下，这种平衡状态可以发展，尽管相同的环境条件同样有利于抑制对流。 这种多重平衡行为在理想化模型中可见，并且与云解析模型中的自聚合有关，PI 假设它与东风波的活跃和抑制阶段有关。这项研究是使用活动期间收集的数据并结合各种数值模型进行的，包括天气研究和预报 (WRF) 模型的云解析版本。 PI 有多种策略以理想化形式表示相关动力学和热力学，通常使用小型双周期域。观察比较使用来自 OTREC 以及早期实地活动（EPIC 和 TEPPS）的数据。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Assessing the Vertical Velocity of the East Pacific ITCZ

评估东太平洋 ITCZ 的垂直速度

• DOI: 10.1029/2021gl096192
• 发表时间: 2022
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Huaman, Lidia;Schumacher, Courtney;Sobel, Adam H.
• 通讯作者: Sobel, Adam H.